HONOLULU — Kids do the darndest things — even to the leader of the free world.

So learned President Obama on Christmas evening.

Vacationing here, Obama and wife Michelle were visiting Marines at a military base in Kaneohe Bay during a holiday dinner in the mess hall when he came upon a baby boy in a red sweater vest and plaid shorts in American red-white-and-blue.

“What’s going on, man? How ya doing?” Obama asked the boy, 8-month-old Cooper Wall Wagner, according to a press pool report.

Obama lifted the baby from the hands of his parents, Capt. Greg Wagner, 25, and Meredith Wagner, 27, and held him over his shoulder. Holding and kissing babies for photo ops, that’s what presidents do.

Acting predictably unpredictable, that’s what babies do.

Deftly outmaneuvering Secret Service, Cooper, hands wandering, reached toward the president’s nose before sticking some of his fingers into the Obama’s mouth — an image captured for posterity by news photographers at the scene.

The president played along merrily.

“See that big nose and say, ‘I want some of that big nose,’” he was heard saying.